Breast cancer remains a major health issue implicating a need for early and accurate detection. X-ray imaging has long been used as a gold standard for both screening and diagnosis. The traditional x-ray modality was mammography “M,” in which the breast is compressed and flattened and a projection x-ray image “Mp” is taken using an x-ray source at one side of the breast and an imaging receptor at the other side, usually with an anti-scatter grid between the breast and the receptor. The receptor for many years was x-ray film, but now digital flat panel imaging receptors have become prevalent.
X-ray breast tomosynthesis “T” has made important inroads, with the widespread acceptance in this country and abroad of systems offered over the last several years by the common assignee, including under the tradename Selenia® Dimensions®. In this modality, the breast also is compressed and flattened but at least the x-ray source moves around the compressed breast and the image receptor takes a plurality of projection images “Tp,” each at a respective angle of the imaging x-ray beam to the breast. The Dimensions® system operates in the tomography mode T to rotate an x-ray source around the patient's flattened breast while a flat panel imaging x-ray receptor takes respective 2D projection tomosynthesis images Tp for each increment of rotation angle over a trajectory that is substantially less than 180°. As one example, the trajectory extends over ±7.5° relative to a 0° position that can but need not be the same as the CC or the MLO position in conventional mammography M. The system processes the resulting 2D projection images Tp (e.g., 15 images Tp) into a 3D reconstructed image of voxel values that can be transformed into reconstructed slice images “Tr” each representing a slice of the breast that has a selected thickness and orientation. Tomosynthesis systems offered by the common assignee respond to operator control to operate in an additional, mammography mode M to produce mammogram images Mp that can be the same as or similar to conventional mammograms. In addition, some of the systems synthesize a mammogram from the reconstructed 3D image of the breast or from images Tr.
Examples of known T and M modes of operation are discussed in U.S. Pat. Nos. 4,496,557, 5,051,904, 5,359,637, 6,289,235, 6,375,352, 6,645,520, 6,647,092, 6,882,700, 6,970,531, 6,940,943, 7,123,684, 7,356,113, 7,656,994, 7,773,721, 7,831,296, and 7,869,563; Digital Clinical Reports, Tomosynthesis (GE Brochure 98-5493, November 1998); D G Grant, “Tomosynthesis: a three-dimensional imaging technique”, IEEE Trans. Biomed. Engineering, Vol BME-19, #1, (January 1972), pp 20-28; U.S. Provisional Application No. 60/628,516, filed Nov. 15, 2004, the benefit of which is claimed in U.S. application Ser. No. 14/744,930 filed on Jun. 19, 2015 and entitled “Matching geometry generation and display of mammograms and tomosynthesis images;” a system announced under the name Giotto Image 3D by I.M.S. Internazionale Medico Scintifica of Bologna, Italy, and a 3D Breast Tomosynthesis system announced by Siemens Healthcare of Germany/USA. Several algorithms for reconstructing slice images from tomosynthesis projections are known, including filtered back-projection and matrix inversion processing, and a proposal has been made to combine information from both. See Chen Y, Lo, J Y, Baker J A, Dobbins III J T, Gaussian frequency blending algorithm with Matrix Inversion Tomosynthesis (MITS) and Filtered Back Projection (FBR) for better digital breast tomosynthesis reconstruction, Medical Imaging 2006: Physics of Medical Imaging, Proceeding of SPIE Vol. 6142, 61420E, (2006).
Whole-body CT x-ray imaging of a patient's thorax also can provide a 3D image of the breast but delivers ionizing radiation to the chest cavity as well. Also, in whole-body x-ray CT the spatial resolution of the breast tends to be lower than in mammography and tomosynthesis because the image matrix includes the entire chest, not just the breast. Overall x-ray dose to the patient tends to be higher. Other modalities also can generate breast images, such as MRI, emission imaging, thermal imaging, and others, but because of various inherent limitations have not been widely used for breast-only imaging. They typically are not suitable for screening, which demands a set of practical attributes that such system may lack, such as good patient flow, relatively low level of patient inconvenience and time, rapid examination, and relatively low cost per patient for the actual examination and for interpretation of the resulting images. CT x-ray imaging of only the breast has been proposed, and can generate high spatial resolution image but the equipment believed to have been in clinical use requires a special table on which the patient lies in the prone position, with a breast protruding downwardly through a table opening and exposed to a nearly horizontal imaging x-ray beam. The breast is not flattened in a coronal plane, so there are no benefits of flattening that mammograms and tomosynthesis images enjoy, such as spreading out lesions for better imaging and reducing skin x-ray dose per unit area. Examples of breast-only x-ray CT are discussed in U.S. Pat. Nos. 3,973,126, 6,748,044, and 6,987,831, 7,120,283, 7,831,296, 7,867,685 and US application No. 2013/0259193 A1, now U.S. Pat. No. 8,842,406 issued on Sep. 23, 2014, proposes CT scanning a standing patient's breast confined by one or two pairs of opposing compression paddles.